1. Field of the Invention
The present invention relates to a clamping device or fastening device for structural components.
2. Description of the Related Art
Fastening devices of this type are used for various technical applications for temporarily securing or holding workpieces. These devices must operate quickly and reliably and must ensure frequent load changes without maintenance over long periods of time.
In this regard, known in the prior art from DE 35 28 337 C2 is a clamping device for structural components in which a clamping rod is a component of a piston which is acted upon by a pressurized fluid, such as air or hydraulic liquid, and is axially displaceable in a cylinder. The end of the clamping rod facing away from the piston is connected to a bolt which supports two pairs of rollers. The rollers of the outer pair of rollers travel in straight slots which extend parallel to the longitudinal axis of the clamping rod. The rollers of the inner pair of rollers travel in arc-shaped slots of a clamping arm which can pivot about an axis. The guide slot may also possibly be curved in an arc-shaped manner.
This configuration is supposed to prevent uncontrollably high clamping forces when self-locking occurs in the end position. However, this construction requires a complicated mechanism and, consequently, its manufacture is also complicated Because of the presence of the guide slot, this clamping device has a large structural width. Because of the direct lever transmission, the travel distance of the piston is long and, thus, the construction of the device is inevitably also long. The bent-lever principle is employed in a modified form in this case.
In order to reach the self-locking position in a clamping device operating in accordance with the bent-lever principle, it is necessary to move the bracket forming a component of the bent-lever arrangement above the upper dead center position. This causes the force in the bracket to be increased theoretically up to infinity. In practice, the force is limited by the elastic deformations in the entire system. However, this means that the system is subject to wear. Moreover, it cannot be ensured that in the case of high clamping forces the clamping arm is actually pivoted past the dead center point. The maximum clamping force is determined by the available energy, particularly compressed air. If the cylinder force prevailing in a compressed air cylinder is not sufficiently great in order to apply the necessary clamping force to the clamping arm, the bracket does not move past the dead center point and, thus, does not travel into the self-locking position.
DE 31 30 942 A1 discloses a clamping device for structural components which operates in accordance with the bent-lever principle. A bracket of resiliently yielding construction is hinged to the free end of a piston rod which is connected to a piston which is acted upon by a pressure medium. The bracket is additionally connected to a rigid bent lever which is coupled 90.degree. offset to a clamping arm. The bracket is constructed in such a way that the distance of the coupling joints to the piston rod and the lever is adjustable.
The resilient bracket has the purpose of preventing infinitely high clamping forces. Consequently, only the clamping force can be limited in this clamping device, while a self-locking position cannot be reached. In addition, the fatigue strength and the durability of the bracket should pose problems. The bracket is also difficult to manufacture. Furthermore, the force limitation is dependent on the spring constant and the spring travel.